The present invention relates generally to fluorescent lamps, and more particularly, to a method for starting a lamp filament, to prolong its life.
The maximum thermal stress of a lamp filament occurs at the moment the lamp is turned on due to the fact that prior to the lamp being turned on it is relatively cold. Under traditional start up of a lamp it is suddenly warmed to a substantially higher temperature. The sudden change in temperature can result in failure of the lamp filament.
It is not uncommon for fluorescent lamps to contain condensed mercury in the filament when the lamp is turned off. When the lamp is turned on the condensed mercury can cause the filament to short out. Furthermore, electrical resistance decreases when the filament is relatively cold. The sudden power surge which is experienced by the lamp when it is turned on can also cause excessive wear and tear on the lamp and filament resulting in failure. Operating temperatures of a filament may reach 11,000.degree. F. and when not in use, in some arctic environments, filaments may be exposed to temperatures as low as minus 54.degree. C.
There exists a need to provide a method in which a lamp may be turned on without inducing the relatively high levels of thermal stress that is common in fluorescent lamps. The method of the present invention uses a "pulse start" duty cycle modulation method in which the lamp is turned on for an instant and then turned off again. This process is repeated several times over a period of a few seconds. Each time the filament is turned on it is allowed to remain on for a relatively longer instant of time, until such time as the filament is powered on continuously. In this manner, the lamp is not experiencing the sudden and continuous high thermal stresses that it otherwise would experience if the filament were turned on and left on continuously during start up. The result is a longer life for a lamp filament using the present invention.